1. Field of the Invention
This invention relates to a brake cable mounting structure suitable for a drum brake structure for a rear wheel. More specifically, this invention relates to a brake cable mounting structure which has a crank mechanism spreading a pair of brake shoes apart and is capable of operating the crank mechanism remotely.
2. Description of Related Art
For example, the brake cable mounting structure for the drum brake is disclosed in the Japanese Patent Application Unexamined Publication Number 6-337027 filed by this applicant. FIGS. 7-10 explain a drum brake device employing this brake cable mounting structure. A pair of brake shoes 110, 120 are moveably mounted on a back plate 100 by shoe hold mechanisms 111, 121. In FIG. 7, lower adjacent ends of the brake shoes 110, 120 are supported by a supporting portion 201 of an almost L-shaped anchor 200 while upper adjacent ends of the brake shoes 110, 120 are connected via an adjuster 130. An upper shoe return spring 160 is extended between the upper adjacent ends of the brake shoes 110, 120 and a lower shoe return spring 160 is extended between the lower adjacent ends of the brake shoes 110, 120, maintaining the abutment of the two brake shoes 110, 120 against the adjuster 130 and the anchor 200.
A crank mechanism 300 comprises a brake lever 320, a strut 330 and a lever pin 310. The crank mechanism 300 is positioned adjacent to the supporting portion 201 of the anchor 200 between the two brake shoes 110, 120. The brake lever 320 comprises two facing long plates. A notched groove 321 formed at the superimposing portion on the right side of the plates in FIG. 8 is functionally engaged with the right brake shoe 110. Referring to FIG. 8, an arc-shaped groove 322 formed on the forked legs on the left side of the two plates receives a cable end nipple 420 of the brake cable 400. A strut 330, integrally formed from a deformed piece of plate, comprises two facing plate portions connected on their upper edges by a bridge 332 and positioned between the two brake shoes 110, 120. A notched groove 331 formed at the superimposing portion on the left side of the strut 330 in the FIG. 8 is functionally engaged with the left brake shoe 120.
The brake lever 320 is inserted from the opposite side of the bridge 332 into a space formed between the two facing plate portions of the strut 330, and upper right ends of the brake lever 320 is pivotally supported relative to the strut 330 through the lever pin 310 acting as the fulcrum as depicted in FIG. 8.
As is evident from FIG. 8, clockwise rotation of the brake lever 320 with the lever pin 310 is restricted by abutting against the bridge 332 of the strut 330. A guide pipe 500 and the brake cable 400, which act as a remote force transmitting member, pass through the back plate 100 for the purpose of engaging and acting upon the arc-shaped groove 322 as an input force portion of the brake lever 320. The guide pipe 500 is depicted in FIGS. 8-10. The guide pipe 500 is so designed that the overhanging portion 501, integrally formed on the intermediate portion of the guide pipe 500, contacts a back of an anchor seat 202 of the anchor 200. An upper portion of the guide pipe 500 penetrates through a hole on the anchor seat 202 and is projected outwardly from the surface of the anchor seat 202. The projected outwardly end portion is widened in opposite directions as shown in FIG. 8; therefore, the guide pipe 500 is integrated with the anchor 200. The widened end 502 of the guide pipe 500 is designed to be partially widened toward both sides of the brake shoes 110, 120. However, the shape of the projected outwardly end portion is not limited to the partially widened shape depicted in FIG. 8 and may be a widened shape in the direction as long as it can secure a thickness of the supporting portion 201 of the anchor 200 without becoming an obstacle to components of the drum brake device.
The brake cable 400 is comprised of an outer casing 430, an inner cable 410 and so on. A large diameter portion of a casing cap 431, fixed with an end of the outer casing 430, abuts against an outer opening end of the guide pipe 500. A small diameter portion of the casing cap 431 fits into a hole of the guide pipe 500. Then, the brake cable 400 is retained on the guide pipe 500 by a wire spring clip 440. A means to retain the casing cap 431 on the guide pipe 500 may be utilized so long as the casing cap 431 is retained on the guide pipe 500 until the operational end (not shown) of the brake cable 400 is attached on a corresponding member. As an alternative, the casing cap 431 may be press fit into the hole of the guide pipe 500 instead of using the clip 440.
The inner cable 410 is slidably inserted into the outer casing 430, and the top side of the inner cable 410 projected out from the casing cap 431 as shown in FIG. 8. The inner cable 410 is passed through the guide pipe 500, where a pin portion 421 of the cable end nipple 420 is secured on the top end of the inner cable 410, which is connected on the arc-shaped groove 322 of the brake lever 320. A dust boot 411 with bellows is positioned and connected between the casing cap 431 and the cable end nipple 420, performing a water proof function into the outer casing 430. For the purpose of maintaining the lower weight of the drum brake, a relatively lighter plate material is used to form the back plate 100. Then, in order to maintain certain high strength requirements for this particular portion: the central portion of the back plate 100, the portion adjacent to the anchor 200 and the connecting portion thereof, a back plate stiffener 101 is provided at the portion on the back plate 100 and is substantially integrated with the back plate 100 such as by welding.
The back plate 100 and the stiffener 101 are fixed on the brake mounting member 150 (e.g., an axle as a member of stationary part of the vehicle) having almost the same outline of the mounting surface as the stiffner 101 by four instalation bolts 140, 140, 141, 141 and corresponding nuts (not shown in the figure). Each of the two bolts 140, 140 at the anchor 200 side has a serration 142 on its intermediate portion. The serrations 142, 142 are pre-press-forced into installation holes 601, 601 formed on a later-described spacer 600 after passing through the anchor seat 202 of the anchor 200, the back plate 100 and the back plate stiffener 101; therefore the anchor seat 202 is temporary fixed on the back plate 100. The right side of the brake lever 320 and the left side of the strut 330 in FIG. 8 are slidably supported by the bolt heads 143, 143 of the bolts 140, 140. Finally, the anchor 200 will be firmly fixed to the brake mounting member 150 when the nuts (not shown in the figure) are tightly screwed with the bolts 140, 140.
Central portions of the back plate 100 and the stiffener 101 are fixed to the brake mounting member 150 via a bearing hub seat (not shown in the figure). Since the bearing hub seat is not extended to the anchor 200 for the purpose of maintaining the lower weight, the spacer 600 with about the same thickness as the bearing hub seat is placed between the stiffener 101 and the brake mounting member 150. This embodiment illustrates the spacer 600 where the serrations 142, 142 formed on the two bolts 140, 140 are press-forced into the installation holes 601, 601 of the spacer 600 and are pre-integrated in the drum brake.
Brake operation of the above-explained structure is explained below. If the operation side of the inner cable 410 (not shown in the figure) is pulled, the intermediate portion of the curved outer casing 430 tends to be deformed back to a straight. The casing cap 431 is supported by the guide pipe 500 and the other side of the outer casing 430 (not shown in the figure) are supported by the corresponding member in order to prevent this deformation, thereby transmitting the pulling force onto the cable end nipple 420. As the pulling force is transmitted to the arc-shaped groove 322 functioning as the input force portion of the brake lever 320, the brake lever 320 rotates counterclockwise in FIG. 8 with the lever pin 310 to press the brake shoe 110, and that reaction force urges the strut 330 to press the brake shoe 120 via the lever pin 310. If such a pressing force goes beyond a tension of the shoe return springs 160, 160, both brake shoes 110, 120 spread apart at the point of abutment on the adjuster 130, thereby making a frictional engagement with the brake drum, not shown in the figure.
In FIG. 7, as the brake drum (not shown in the figure) rotates clockwise, the brake shoe 110 becomes supported by the supporting portion 201 of the anchor 200, and the brake shoe 120 becomes supported by the adjuster 130, thereby generating a braking force. As the brake drum rotates counterclockwise, the brake shoe 120 becomes supported by the supporting portion 201 of the anchor 200, and the brake shoe 110 becomes supported by the adjuster 130, thereby generating a braking force. Accordingly, both brake shoes 110, 120 have self-servo function even if the brake drum rotates in either direction, i.e., functioning as a duo-servo (DS) type drum brake.
The above-conventional drum brake suffers from the following drawbacks and deficiencies.
The guide pipe 500 is designed so that the overhanging portion 501 contacts the back (the back plate 100 side) of the anchor seat 202 of the anchor 200, and the upper portion of the guide pipe 500 is penetrated through the hole on the anchor seat 202 in FIG. 8. Former projected outwardly end portion is widened. With this structure, an effective stroke of the brake cable 400 is restricted between the lower end surface of the brake lever 320 and the widened end 502 of the guide pipe 500. If the distance (brake off-set) H from the brake mounting surface to the center of the brake shoes 110, 120 in the width direction is small, it becomes difficult to design the layout of the [portion where the] brake cable mounting section and the crank mechanism 300.
The overall length of the guide pipe 500 must be longer, which is another disadvantage when considering the cost.
When in brake operation, the anchor 200 receives the brake force of the brake shoes 110, 120 and the operational reaction force on the outer casing 430 via the guide pipe 500. Therefore, the anchor 200 needs to be stronger which is another disadvantage in considering the weight and cost.